Control circuit and method for estimating an output current of a transformer

Abstract

A control signal circuit for estimating a current output from a transformer. The control signal circuit includes a converter circuit configured to receive a signal corresponding to a current input to the transformer and output, over a half line cycle, a plurality of values corresponding to the current output from the transformer. The half line cycle corresponds to a period that the transformer is connected to an input voltage. An output current estimator is configured to accumulate the values output from the converter circuit over the half line cycle, determine an average value of the current output from the transformer over the half line cycle, and output the average value of the current output from the transformer over the half line cycle.

What is claimed is: 
     
         1 . A control signal circuit for estimating a current output from a transformer, the control signal circuit comprising:
 a converter circuit configured to (i) receive a signal corresponding to a current input to the transformer and (ii) output, over a half line cycle, a plurality of values corresponding to the current output from the transformer, wherein the half line cycle corresponds to a period that the transformer is connected to an input voltage; and   an output current estimator configured to (i) accumulate the values output from the converter circuit over the half line cycle, (ii) determine an average value of the current output from the transformer over the half line cycle, and (iii) output the average value of the current output from the transformer over the half line cycle.   
     
     
         2 . The control signal circuit of  claim 1 , wherein the period that the transformer is connected to the input voltage corresponds to an on time of a switch connected to the transformer. 
     
     
         3 . The control signal circuit of  claim 1 , wherein the plurality of values correspond to an area of the current output from the transformer over the half line cycle. 
     
     
         4 . The control signal circuit of  claim 3 , wherein the converter circuit is configured to calculate the area of the current output from the transformer over the half line cycle using (i) a sample of the current input to the transformer, (ii) the half line cycle, (iii) a turn ratio of the transformer, and a period that the transformer is not connected to the input voltage. 
     
     
         5 . The control signal circuit of  claim 4 , wherein, to calculate the area of the current output from the transformer over the half line cycle, the converter circuit is configured to calculate the area according to 
       
         
           
             
               
                 
                   
                     
                       I 
                       p 
                     
                      
                     
                       ( 
                       
                         
                           T 
                           ON 
                         
                         2 
                       
                       ) 
                     
                   
                   N 
                 
                 * 
                 
                   
                     T 
                     OFF 
                   
                    
                   
                     ( 
                     t 
                     ) 
                   
                 
               
               , 
             
           
         
       
       wherein I p  corresponds to the sample of the current input to the transformer, T ON  corresponds to the half line cycle, N corresponds to the turn ratio of the transformer, and T OFF (t) corresponds to the period that the transformer is not connected to the input voltage. 
     
     
         6 . The control signal circuit of  claim 1 , further comprising an accumulator configured to (i) compare the average value of the current output from the transformer over the half line cycle to a reference current and (ii) output an error signal corresponding to a difference between the average value of the current output from the transformer over the half line cycle to a reference current. 
     
     
         7 . The control signal circuit of  claim 6 , further comprising a controller configured to calculate a duty cycle based on the error signal output from the accumulator. 
     
     
         8 . The control signal circuit of  claim 7 , further comprising a pulse width modulation generator configured to, based on the duty cycle calculated by the controller, selectively control the period that the transformer is connected to the input voltage. 
     
     
         9 . The control signal circuit of  claim 1 , wherein the converter circuit includes an analog to digital converter. 
     
     
         10 . A method for estimating a current output from a transformer, the method comprising:
 receiving a signal corresponding to a current input to the transformer;   outputting, over a half line cycle, a plurality of values corresponding to the current output from the transformer, wherein the half line cycle corresponds to a period that the transformer is connected to an input voltage;   accumulating the plurality of values over the half line cycle;   determining an average value of the current output from the transformer over the half line cycle; and   outputting the average value of the current output from the transformer over the half line cycle.   
     
     
         11 . The method of  claim 10 , wherein the period that the transformer is connected to the input voltage corresponds to an on time of a switch connected to the transformer. 
     
     
         12 . The method of  claim 10 , wherein the plurality of values correspond to an area of the current output from the transformer over the half line cycle. 
     
     
         13 . The method of  claim 12 , wherein calculating the area of the current output from the transformer over the half line cycle includes calculating the area using (i) a sample of the current input to the transformer, (ii) the half line cycle, (iii) a turn ratio of the transformer, and a period that the transformer is not connected to the input voltage. 
     
     
         14 . The method of  claim 13 , wherein calculating the area of the current output from the transformer over the half line cycle includes calculating the area according to 
       
         
           
             
               
                 
                   
                     
                       I 
                       p 
                     
                      
                     
                       ( 
                       
                         
                           T 
                           ON 
                         
                         2 
                       
                       ) 
                     
                   
                   N 
                 
                 * 
                 
                   
                     T 
                     OFF 
                   
                    
                   
                     ( 
                     t 
                     ) 
                   
                 
               
               , 
             
           
         
       
       wherein I p  corresponds to the sample of the current input to the transformer, T ON  corresponds to the half line cycle, N corresponds to the turn ratio of the transformer, and T OFF (t) corresponds to the period that the transformer is not connected to the input voltage. 
     
     
         15 . The method of  claim 10 , further comprising:
 comparing the average value of the current output from the transformer over the half line cycle to a reference current; and   outputting an error signal corresponding to a difference between the average value of the current output from the transformer over the half line cycle to a reference current.   
     
     
         16 . The method of  claim 15 , further comprising calculating a duty cycle based on the error signal. 
     
     
         17 . The method of  claim 16 , further comprising, based on the duty cycle, selectively controlling the period that the transformer is connected to the input voltage. 
     
     
         18 . The method of  claim 10 , receiving the signal corresponding to the current input to the transformer and outputting the plurality of values corresponding to the current output from the transformer include using an analog to digital converter to receive the signal and output the plurality of values.